1. Field of Invention
This invention relates to a combined muscle stimulation, pacing and defibrillation apparatus and its method of operation for detecting abnormalities of a patient's heart and, in response to such detection, administering defibrillation therapy. More particularly, this invention relates to a pacing apparatus and method that employs defibrillation therapy which comprises the coordination, control and generation of stimulation pulses to both the patient's heart and to a muscle graft that has been previously wrapped around the heart, with means being provided to insure that the defibrillation therapy is most efficient achieved.
2. Description of the Prior Art
Severe chronic cardiac insufficiency arising from cardiac disease or injury shortens and degrades the quality of life of many patients. One form of severe chronic cardiac insufficiency, congestive heart failure, is a pathophysiological state in which cardiac output is inadequate to meet physiological requirements of the body. The mortality rate for congestive heart failure is greater than 50% within 5 years of onset. Treatments for severe chronic cardiac insufficiency include heart transplants, artificial heart implants and cardiomyoplasty. Cardiac transplantation, using cyclosporine to inhibit tissue rejection, is a very successful technique for prolonging a cardiac patient's life, improving the survival rate to 80% at 1 year. However, the transplant operation is very expensive and heart availability is limited. The artificial heart has had very limited success.
Dynamic cardiomyoplasty is a surgical and electrical therapeutic technique used to overcome or at least alleviate cardiac insufficiency. This technique consists of using a skeletal muscle flap which is dissected from a patient, while maintaining its neural tissues and neurovascular structures, surgically placed around the patient's heart. An electrical stimulation device, with an electrical pulse generator and intramuscular electrodes, is implanted for performing muscle electrical stimulation in synchrony with ventricular systole to support cardiac pumping.
Repeated stimulation of the skeletal muscle transforms it into a fatigue-resistant muscle suitable for chronic ventricular assistance, enabling dynamic cardiomyoplasty. The skeletal muscle is then trained to function so as to assist cardiac muscle to increase the patient's cardiac output. Sequential and progressive skeletal muscle electrical stimulation causes glycolytic muscle fibers, predominant in skeletal muscle, to take the form of oxidative fibers. Oxidative fibers are resistant to fatigue and have histochemical and biochemical characteristics of myocardium.
Presently, cardiomyoplasty patients suffering from ventricular fibrillations are treated by one of several methods, depending on the circumstances at the time of the onset of fibrillation. Each of these methods has several disadvantages. Ventricular fibrillations occurring in the hospital must be first confirmed by doctors or paramedical personnel. Standard high energy defibrillation shocks are then applied to the patient. Of course, these shocks must be applied by people having special training. If the ventricular fibrillation occurs outside a hospital, the patient must wait for trained medical help to arrive and apply the high energy shocks as discussed above.
Commonly assigned U.S. Pat. No. 5,251,621, incorporated herein by reference, proposes a therapy for preventing and terminating cardiac arrhythmias which may lead to ventricular fibrillation and sudden death in patients suffering from congestive heart failure. The proposed therapy combines antiarrhythmic pacing of various forms with skeletal muscle graft stimulation. Muscle graft stimulation increases cardiac output, aortic pressure and, therefore, perfusion of the heart to alleviate myocardial ischemia and ameliorate arrhythmias. The device performs pacing, defibrillation and skeletal muscle stimulation is disclosed in commonly assigned U.S. Pat. No. 5,251,621. However this patent only teaches the stimulation of the skeletal muscle in synchronism with arrhythmia pacing in order to increase cardiac output.
Commonly assigned U.S. Pat. Nos. 4,796,630; 5,178,140; and 5,215,083 disclose devices performing both pacing and defibrillating functions. None of the cited references disclose, or even suggest, a device capable of performing defibrillation therapy which includes the stimulation of the skeletal muscle as part of the therapy.